Modular cooling system

ABSTRACT

A heat exchange unit for use in a modular heat exchange system including at least one first heat exchanger having a closed circuit for cooling fluid at least one air cooler located upstream of the first heat exchanger, and at least one first fan arrangement operable to cause air to pass through the at least one air cooler and the at least one first heat exchanger, at least one channel providing cooling fluid interconnection between the first heat exchanger and, when in use in the modular heat exchange system, a heat exchanger in at least one other heat exchange unit.

FIELD OF THE INVENTION

The present invention generally relates to cooling systems, and in particular a fluid cooling heat exchanger in which fluid is cooled substantially by convective heat transfer. The invention is particularly suited to cooling systems for relatively large volumes such as; for example, a part of an air conditioning system in large office buildings or commercial refrigeration systems.

BACKGROUND OF THE INVENTION

Heating and cooling systems are used in most modern premises to maintain the temperature in those premises within predetermined limits. One type of system for the cooling of large buildings is a cooling system that incorporates a roof top mounted heat exchanger. In this type of system, the thermal energy from air in the building is transferred through one or more interconnected heat exchange units within the building to a roof mounted heat exchange unit. In the building, a refrigerant is used to cool air as the air passes through a heat exchange unit (an evaporator). The heated refrigerant is then passed to another heat exchange unit (a condenser) wherein heat is extracted from the refrigerant using a heat exchange fluid such as water. The heated water is usually then transferred to the roof top mounted heat exchanger which uses ambient, air at the roof of the building to cool the water in preparation for further use. The most commonly installed roof top mounted heat exchanger is a type known as an “open” system that incorporates many disadvantages, such as the propensity to generate and transmit sufficient levels of the bacterium known as legionella kneumophilia to cause Legionnaire's disease in people that inhale the bacterium.

Large buildings typically require the removal of a large heat load particularly during the height of summer. Accordingly, roof top mounted heat exchangers are generally configured to provide a sufficient heat exchange capacity to cope with the largest expected heat load.

In view of the problems associated with “open” roof top mounted heat exchangers, there is an increasing trend for building owners to consider “closed” roof top mounted heat exchangers or heat exchanger arrangements wherein the cooling fluid remains within a closed circuit and is not exposed to the atmosphere. A closed circuit heat exchanger avoids the problems associated with generating and transmitting the legionella pneumophilia bacterium. However, closed circuit heat exchangers suffer a range of different problems including a substantially reduced heat exchange capacity as compared with an open roof top mounted heat exchanger of similar dimension and weight.

Closed circuit heat exchangers typically use large planar tube and fin modules that include fluid carrying passages with fan arrangements to pass air through and/or over the planar modules to meet the desired heat exchange requirement. Construction of these types of heat exchangers necessitate specialised equipment to move, mount and assemble the structure. Further, specialised structural support members are generally required on a building roof to distribute the weight of a closed circuit heat exchanger across the roof surface and a significant amount of space on the roof of the building is required to accommodate the relatively large size. Typically, closed circuit heat exchangers are constructed “off site”, transported to the installation site on a large truck and lifted by crane from the truck to the rooftop for installation and commissioning. The cost and inconvenience of arranging transport and cranes is significant and increases the cost of the overall installation.

In the instance of installing a large closed circuit heat exchanger, it is sometimes necessary to situate a large crane on a street next to the building to lift the tower to the building roof top. This may require the street to be closed during the installation which generally restricts installation to periods of time of relatively low street usage. Of course, this generally relates to night times or weekends which increase the rate of pay for any installation staff and hence increases the overall cost of installation.

Accordingly, it is desirable to provide an alternative closed circuit heat exchanger that is more compact than existing arrangements and avoids, or at least ameliorates, the cost and difficulty associated with transporting, installing and supporting a closed circuit heat exchange system.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a heat exchange unit for use in a modular heat exchange system including at least one first heat exchanger having a closed circuit for cooling fluid, at least one air cooler located upstream of the first heat exchanger, and, at least one first fan arrangement operable to cause air to pass through the at least one air cooler and the at least one first heat exchanger, at least one channel providing cooling fluid interconnection between the first heat exchanger and, when in use in the modular heat exchange system, a heat exchanger in at least one other heat exchange unit.

In one embodiment, the air cooler, when in use, has air passing through it caused by a fan arrangement, which may be the first fan arrangement. In this embodiment the air that passes through the air cooler is cooled. The cooled air then passes through and/or over the closed circuit heat exchanger.

In another embodiment, the first closed circuit heat exchanger is configured in a substantially cross sectional tubular arrangement wherein the first fan arrangement is operable to cause air to pass longitudinally through the internal space of the substantially tubular arrangement of the first closed circuit heat exchanger. Of course, air may also pass through the walls of the substantial tubular arrangement thereby assisting the heat exchange process.

In a further embodiment, a second heat exchanger having a closed circuit for cooling fluid is arranged with the first closed circuit heat exchanger such that they form a substantially cross sectional tubular arrangement with an internal space through which air can pass.

The fan arrangement can be situated in various locations relative to the first closed circuit heat exchanger. However, in one exemplary embodiment, the direction of the air flow resulting from the operation of the first fan arrangement is in a direction that is substantially aligned with the longitudinal axis of the tubular arrangement, or is substantially aligned with the longitudinal axis of the arrangement of the first and the second closed circuit heat exchangers.

Of course, a modular heat exchange system according to the present invention may include one or more fan arrangements that cause air to pass through the first heat exchanger. In those embodiments including two or more fan arrangements, the direction of air flow of each fan arrangement may be substantially aligned. In exemplary embodiments of the present invention, the modular heat exchange system, includes a single fan arrangement at one end of the tubular arrangement for forcing air through the first closed circuit heat exchanger.

When the first closed circuit heat exchanger is formed in a substantially tubular arrangement, it may have various cross-sectional shapes perpendicular to its nominal longitudinal axis. Suitable shapes include substantially square, hexagonal, octagonal, star-shaped, triangular or similar. In one embodiment, the tubular arrangement has a generally circular or oval cross-section perpendicular to its nominal longitudinal axis. In another exemplary embodiment, the substantially tubular arrangement has a generally square or rectangular cross-section perpendicular to the longitudinal axis. In this embodiment, the generally square or rectangular cross-section has one or more arcuate corners.

The structure of the tubular arrangement can circumferentially extend wholly or partially around the longitudinal axis of the tubular arrangement. Of course, in some arrangements the tubular arrangement forms a continuous body around the longitudinal axis. This forms an enclosed tube around the longitudinal axis of the tubular arrangement. In other exemplary embodiments, the first closed circuit heat exchanger could operate with the substantially tubular arrangement and a heat exchange body forming the wall of the tubular arrangement extending partially around its longitudinal axis. This would provide a circumferential gap in the body of the tubular arrangement. As can be appreciated, the greater the tubular arrangement of the heat exchange body extends around the longitudinal axis, the more efficiently the configuration utilises the air flow from the fan arrangement for cooling the cooling fluid contained in the fluid passages in the walls of the tubular arrangement. It is therefore preferable that the tubular arrangement of the heat exchange body extends around its longitudinal axis to the greatest extent possible to substantially form an enclosure around the longitudinal axis. Of course, two or more separate closed circuit heat exchangers could be substantially butted together, or situated in close proximity, to form a generally tubular enclosure through which air passes.

The inclusion of a gap in the circumference of the tubular arrangement could occur for numerous reasons. In one embodiment, a gap is provided for the provision of a header arrangement through which cooling fluid enters and exits the closed circuit forming the walls of the tubular arrangement. The header may be provided at one or both of two spaced apart longitudinal ends each of which extend generally parallel to the longitudinal axis of the tubular arrangement. The closed circuits for the cooling fluid circumferentially extend between these ends. In some arrangements, only one of the longitudinal ends includes a header, the other end having connecting sections having a closed end. In other arrangements, each of the longitudinal ends includes a header thereby allowing fluid to flow between the headers or in separate sections of the heat exchange body connected to the respective headers.

In one exemplary embodiment, cooling fluid flows through the first closed circuit heat exchanger by entering the header arrangement at the top end of the first closed circuit heat exchanger and exiting the header arrangement at the base end of the first closed circuit heat exchanger. In this embodiment, the fan arrangement is preferably configured to cause air to flow first from the bottom and through the substantially enclosed space within the tubular heat exchanger unit oriented vertically with the air being caused to flow axially upwardly to exit from the top end of the first closed circuit heat exchanger. In another exemplary embodiment a fan arrangement is located proximate to, or at the top of, the first closed circuit heat exchanger. Either of these embodiments provides a counter current heat exchange arrangement where the air flow and cooling fluid flow are in different directions.

A large variety of types of fluid carrying passages for the first closed circuit heat exchanger could be used including plate, plate-fin, spiral, tube, double pipe, coil or similar. In one exemplary embodiment, the heat exchanger includes a closed circuit formed by a plurality of circumferentially arranged passages that are generally laterally arranged in the heat exchange body relative to the longitudinal axis.

The cooling fluid used in the first closed circuit heat exchanger can vary depending on the particular cooling requirements. In some applications, the cooling fluid is water or oil. In other applications, the cooling fluid is selected from a refrigerant gas such as ammonia, Freon or carbon dioxide.

In yet another embodiment, the first closed circuit heat exchanger is a microchannel heat exchanger with fluid passages that are substantially smaller than those of standard tube and fin closed circuit heat exchangers. In one exemplary arrangement having a closed circuit microchannel heat exchanger, the cooling fluid is supplied through a substantially horizontal supply header and is passed from the closed circuit microchannel heat exchanger through another substantially horizontal return header. In one arrangement the supply header is located at or near the top of the closed circuit microchannel heat exchanger and the return header is located at or near the bottom of the closed circuit microchannel heat exchanger such that cooling fluid passes into the closed circuit microchannel heat exchanger at or near the top and passes once through the closed circuit microchannel heat exchanger by the action of gravity and subsequently passing out through the return header, at or near the bottom.

In another embodiment the supply header and the return header are located at or near the vertical sides of the closed circuit microchannel heat exchanger. Typically, cooling fluid flows in through the supply header and passes through the fluid passages of the closed circuit microchannel heat exchanger to the return header where the cooling fluid may flow out of the return header.

In a further exemplary embodiment, a closed circuit microchannel heat exchanger includes a first and second closed circuit microchannel heat exchange modules arranged such that the surfaces of the first module are substantially parallel to the surfaces of the second modules and aligned such that the flow of cooled air passes through the first module and subsequently through the second module. In this embodiment cooling fluid is arranged to flow through the first module and subsequently through the second module.

It should be noted that the at least one first heat exchanger of the present invention has a closed circuit for the cooling fluid to ensure that the cooling fluid is prevented from exposure to the atmosphere, and in particular, to the air passing through the cooling fluid heat exchanger. In instances where water is used as the cooling fluid, this separation of cooling fluid as it passes through the heat exchanger (referred to as a “closed circuit” heat exchanger) from the air passing through the heat exchanger removes the risk of the distribution of airborne legionella bacterium. In practice, the closed circuit is likely to form part of a loop within a cooling system where the cooling fluid is transported from a location where the fluid is used to absorb thermal energy and subsequently transported to the cooling fluid heat exchanger in order to remove the absorbed thermal energy from the cooling fluid.

In some environments where the ambient external temperature can exceed 30° Celsius, the use of a closed circuit heat exchanger system cooled with ambient air is unable to remove sufficient thermal energy for the air conditioning system to form a commercially viable configuration. In these arrangements, convective cooling is therefore only possible by providing an impractically large primary heat exchanger which is usually, a commercially non-viable prospect.

In high ambient temperature environments, cooling the ambient air prior to passing same through a heat exchanger results in a commercially viable configuration.

In order to cool air flowing through the first heat exchanger, the air cooler may be located over or proximate to one or more air inlets through which the fan arrangement causes cooled air to pass through the first closed circuit heat exchanger. In one embodiment, the fan arrangement draws cooled air through the walls of the first closed circuit heat exchanger. In this embodiment, at least one air cooler is arranged radially outwardly of the walls of the first closed circuit heat exchanger.

The air cooler may have a number of arrangements. In one exemplary embodiment, the air cooler includes a moisture absorbent material in the form of moisture absorbent pads, that are, in use, maintained moist such that air passing through the cooler is cooled by the action of evaporation prior to passing over a portion of the closed circuit in the first heat exchanger. It has been found that the use of an air cooler with moisture absorbent material significantly improves the cooling capacity of the heat exchange unit. Accordingly, the same cooling capacity can be produced from a substantially smaller heat exchange unit, as compared with a heat exchange unit without an air cooler, thereby reducing the capital cost of the heat exchange unit for a particular thermal load.

In one embodiment, the moisture absorbent material includes a plurality of fluted apertures and is arranged generally parallel to one or more of the walls of the body of the first closed circuit heat exchanger. In this arrangement, the air cooler may include a fluid dispenser that dispenses moisture onto the moisture absorbent material thus maintaining it moist during operation of the heat exchange unit.

In another embodiment, the heat exchange unit includes a moisture recirculation system for evaporatively cooling air, the system including a moisture distribution arrangement which, in use, distributes moisture to an upper portion of the moisture absorbent material in the air cooler; a trough disposed below the lower most portion of the moisture absorbent material in the air cooler for initially collecting moisture run-off; a sump in fluid communication with the trough for collecting and storing said run-off; and a pump in fluid communication with the sump which, in use, transfers moisture from the sump to the moisture absorbent material.

In an embodiment, the moisture absorbent material supports an adiabatic process when it is maintained moist with water. Although water is inexpensive and generally in plentiful supply, in recent times the need to conserve water as much as possible has become well known particularly in view of water restrictions that have been imposed in many parts of the world that are experiencing extended drought conditions. Of course, the water may include additives such as anti-microbial agents and/or any other additives to improve the operation of the water recirculation system.

In another embodiment, the trough disposed below the lower most portion of the moisture absorbent material is dimensioned such that per unit length the trough will collect and/or hold substantially less run-off as compared with existing trough arrangements that act as the run-off collection and storage means. The trough may act as a temporary and intermediate storage location for run-off water until such time that the water collected in the trough can be transferred to the sump. As the sump is not required to extend the full length of the moisture absorbent material, it may be substantially smaller and hold substantially less water as compared with existing trough arrangements whilst still maintaining a positive head of pressure at the pump intake.

In this particular embodiment, a reduced sump size (as compared with usual arrangements) assists in reducing the operational weight of the heat exchange unit which is a factor requiring consideration with respect to providing adequate structural support for the heat exchange unit.

In an embodiment of the invention, an external source of make-up water (to replace water that is evaporated during the air cooling process) is in fluid communication with the moisture recirculation system. In this embodiment, the supply of make-up water is controlled by a valve which is activated and deactivated in accordance with a control system that determines the requirement for make-up water. The make-up water may be supplied to the sump. Alternatively, and preferably, the make-up water is supplied directly to the moisture absorbent material and as run-off water is collected and passed to the sump, the level of stored water in the sump increases.

In one embodiment, the pump transfers moisture from the sump to the moisture absorbent material by pumping moisture from the sump to the moisture distribution arrangement.

In this latter, embodiment, when water is used as the moisture, a standard float valve arrangement is used to monitor the water level in the sump thus ensuring that a positive head of pressure is maintained at the pump intake. The external water is not supplied to the sump but rather is applied directly to the moisture absorbent material of the air cooler and may be transferred through the water distribution arrangement that distributes water to the upper portions of the moisture absorbent material. As a result of by-passing the sump, the make-up water is directly deposited where it is needed without the normal delay associated with filling the sump and then transferring the make-up water from the sump, through the pump and subsequently to the water distribution arrangement. Of course, the time required to increase the water level in a relatively small sump is substantially less as compared with existing trough arrangements. However, applying external make-up water directly to the moisture absorbent material reduces the time required to saturate the moisture absorbent material.

Of course, opening the float valve which allows the ingress of external (make-up) water into the water recirculation system ultimately increases the sump contents as water runs off the moisture absorbent material which in turn fills the sump and eventually acts to close the float operated valve.

Of course, this supply of external water by the valve to the moisture absorbent material may occur through a separate water distribution system as compared with the water distribution system that is in fluid communication with the sump and pump arrangement. However, there is no reason why the same water distribution arrangement could not be used for both recirculated water and external make-up water and in an embodiment of the invention, the make-up water is introduced into the water conduit that extends from the pump outlet to the water distribution system disposed above the moisture absorbent material.

Embodiments of the invention that incorporate intermediate and temporary run-off water collection arrangements with any collected run-off water being directed to a sump for subsequent transfer by pump to a water distribution arrangement disposed above the moisture absorbent material may substantially reduce the amount of wasted water particularly where the dimensions of the sump and trough are substantially reduced as compared with existing trough arrangements. In particular, by using a trough as an intermediate run-off water collection arrangement below the moisture absorbent material and subsequently transferring run-off water to a sump, the sump may be dimensioned significantly smaller than standard trough arrangements whilst still maintaining the necessary head of pressure at the pump intake.

Of course, where it is possible to operate a water recirculation system with a smaller sized sump, in addition to the reduced operational weight of the system, the amount of wasted water is commensurately reduced as the regular dumping cycle will only result in the dumping of a smaller quantity of water.

In an embodiment of the invention that directs make-up water to a point in the water recirculation system subsequent to the outlet of the pump and prior to the inlet of the water distribution arrangement, the amount of time required to saturate the moisture absorbent material from a dry condition is reduced as compared with an arrangement where the make-up water is directed into a sump or trough in the first instance and subsequently pumped to the water distribution arrangement. Therefore, where make-up water is directed to a point between the outlet of the pump and the inlet of the water distribution arrangement, the time required to transition a cooling apparatus from dry mode to wet mode is substantially reduced as compared with existing systems. Where this delay is sufficiently reduced, the requirement to pre-emptively commence operation of the water recirculation system in anticipation of worsening climatic conditions is obviated. A more responsive water recirculation system that can transfer from dry to wet mode as quickly as possible has the associated benefit of avoiding more instances of false priming of the air cooling system and hence avoiding the wastage of water in those instances where a false priming would otherwise occur.

According to a further aspect, the present invention provides a method of circulating moisture for evaporatively cooling air in the moisture recirculation system, the method including the steps of applying the moisture to the upper portion of the moisture absorbent material, initially collecting the moisture run-off in the trough disposed below the moisture absorbent material, transferring the run-off moisture from the trough to the sump for storage, transferring the moisture from the sump to the moisture absorbent material, and monitoring the moisture level in the sump and in the event that the moisture level in the sump falls below a predetermined threshold, activating supply from an external source of make-up moisture and supplying said make-up moisture directly to the moisture absorbent material.

According to another aspect of the present invention, there is provided a modular heat exchange system including at least two heat exchange units each having a first heat exchanger having a closed circuit for cooling fluid, at least one air cooler forming a second heat exchanger located upstream of the first heat exchanger, and at least one first fan arrangement operable to cause air to pass through the at least one air cooler and the first heat exchanger, wherein the rust heat exchangers of each of the at least two the heat exchanger units are in fluid communication allowing flow of cooling fluid therebetween.

In some embodiments, from a cooling fluid flow perspective, the first heat exchanger is arranged in parallel or in series with one or more further first heat exchangers. In this exemplary embodiment, each of the first closed circuit heat exchangers effectively forms a heat exchange unit and one, or a small number, of heat exchange units can be designed and constructed. Each heat exchange unit will have a predetermined heat exchange capacity. One or more heat exchange units can therefore be used in a modular heat exchange system to accommodate the heat loading for a selected application or use. For example, when used in a cooling system for a building, a number of heat exchange units could be selected to accommodate the maximum heat loading from the building during the maximum temperature period during summer, based upon the heat exchange capacity of each unit.

In another embodiment, the heat exchange unit includes a second heat exchanger aligned substantially in series with the first heat exchanger from an air flow perspective thereby, forming a heat exchanger stack. In this embodiment, an increased heat exchange capacity is achieved by use of a stack of heat exchangers although placing two or more heat exchangers in air flow series to form a stack is expected to increase the resistance of air flow through the stack and hence require a substantially greater supply of air. This in turn increases the electrical energy consumption of the fan arrangement as it is required to cause air to pass through an arrangement presenting greater air flow resistance as compared with a single heat exchanger.

In yet another aspect, the present invention provides a method of installation of a modular heat exchange system including transporting one or more heat exchange units to an installation location, connecting the one or more heat exchange units to a cooling fluid supply, connecting the one or more heat exchange units to a power supply, and activating the modular heat exchange system.

Typically, a heat exchange unit would be relatively small in size as compared with roof top mounted heat exchangers using planar tube and fin heat exchangers. In one embodiment, heat exchange units are sized to fit into the goods lift of a building. In this way, each individual heat exchange unit could be transported to the roof of the building via the goods lift and thereafter the modular heat exchange system could be assembled on the rooftop by connecting each of the individual heat exchange units. In this respect, each heat exchange unit would be connected during installation to provide the overall required heat exchange capacity for that building.

Maintenance of such a modular system is more flexible than existing systems as any faulty heat exchange unit could be isolated and replaced without de-commissioning the remaining heat exchange units. Isolating a faulty unit and replacing or repairing the damaged heat exchange unit whilst the remaining heat exchange units continue to function provides a significant benefit with respect to the convenience with which repairs to a heat exchange system may be effected.

Roof top mounted heat exchangers are generally custom constructed to meet the heat demand of a particular building. Accordingly, each component part such as the first heat exchanger, fan arrangement or the like can in some instances be custom fabricated for that particular building. As will be appreciated, this can lead to very large structures being constructed on building rooftops. The present invention can in some embodiments be custom constructed.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the figures of the accompanying drawings, which illustrate exemplary embodiments of the present invention, wherein:

FIG. 1 is schematic diagram illustrating the main components of a closed circuit cooling system incorporating an air-cooled roof top mounted heat exchanger.

FIG. 2 is a schematic diagram illustrating a further form of a closed circuit cooling system incorporating an air-cooled roof top mounted heat exchanger having air cooler including moisture absorbing pads.

FIG. 3 is a plan view of a closed circuit heat exchanger coil according to one exemplary embodiment of the present invention.

FIG. 4 is a front elevation view of the closed circuit heat exchanger coil of FIG. 2.

FIG. 5 is a right side elevation view of the closed circuit heat exchanger coil of FIG. 2.

FIG. 6 is a perspective view of a header arrangement and coil ends of the closed circuit heat exchanger coil of FIG. 2.

FIG. 7 is a front elevation view of a first exemplary embodiment of a heat exchange unit according to the present invention.

FIG. 8 is a front elevation view of a second exemplary embodiment of a heat exchange unit according to the present invention.

FIG. 9 is plan view of a single heat exchange unit of a modular heat exchange system, according to an exemplary embodiment of the present invention.

FIG. 10 is plan view of a modular heat exchange system having two heat exchange units according to an exemplary embodiment of the present invention.

FIG. 11 is plan view of a modular heat exchange system having three heat exchange units according to another exemplary embodiment of the present invention.

FIG. 12 is plan view of a modular heat exchange system having four heat exchange units according to a further exemplary embodiment of the present invention.

FIG. 13 is a plan view of a heat exchange unit according to one exemplary embodiment.

FIG. 14 is a plan view of a heat exchange unit according to another exemplary embodiment shown without air coolers.

FIG. 15 is a front elevation view of an embodiment of the heat exchange unit with a duplex heat exchanger arrangement.

FIG. 16 is a view of the heat exchange unit according to FIG. 13 shown with a different orientation.

FIG. 17 is a view of the heat exchange unit according to FIG. 14 shown with a different orientation.

FIG. 18 is a front elevation view of an embodiment of the heat exchange unit.

FIG. 19 is a view of an embodiment of a closed circuit heat exchanger showing a planar side of the heat exchanger body.

FIG. 20 is a side view of the closed circuit heat exchanger of FIG. 19.

FIG. 21 is a top view of a modular heat exchange system with eight heat exchange units.

FIG. 22 is a diagrammatic representation of an embodiment of a heat exchange unit incorporating an existing moisture recirculation system;

FIG. 23 is a diagrammatic representation of an embodiment of a cooling system including a moisture recirculation arrangement according to an embodiment of the invention; and

FIG. 24 is a diagrammatic representation of the cooling system of FIG. 23 providing a perspective view of some of the components detailed in FIG. 23.

DETAILED DESCRIPTION

Referring to FIG. 1, there is shown a schematic diagram of a conventional closed circuit cooling system arrangement (18) which provides cooled air to a building (20). This closed circuit cooling system arrangement (18) includes a roof top mounted heat exchanger (23) which typically includes substantially planar primary heat exchange plates (27, 27A).

The illustrated closed circuit cooling system arrangement (18) comprises a heat exchanger system (21) located at the base of the building (20) designed for exchanging thermal load between an enclosed loop of refrigerant fluid (22) and a water circuit (30). The water circuit (30) is linked to the internal air conditioning system of the building (not shown). Air in the building (20) is generally cooled by drawing air through a duct in which a portion of the chilled water circuit (30) resides. Thermal energy from the air is transferred to the chilled water circuit (30) cooling the air in the building (20). The enclosed loop of refrigerant fluid (22) is used to cool the water circuit (30). This is achieved by passing the refrigerant fluid through a heat exchanger (28) where it absorbs thermal energy from the water circuit (30) which is also moving through the heat exchanger (28) in a counter-current flow. The flow of refrigerant fluid through the circuit (22) is driven by a compressor (24) and regulated by expansion valve (26).

A roof top mounted heat exchanger (23) is situated on the roof of the building (20). The illustrated roof top mounted heat exchanger (23) consists of air cooled condensers (27, 27A), which are configured with electrically driven fans (29 and 31) located at the top of the condensers (27, 27A), which draws air through the condenser coils of (27, 27A) via side air inlets (not illustrated) and expelling the drawn air through the fans (29 and 31) and out above the roof top mounted heat exchanger (23). It is usual for roof top mounted heat exchanger (23) to be placed upon the roof of a building (10) as heat exchangers are usually large and due to the use of large fans, (29, 31) emit a substantial amount of noise during operation. The refrigerant fluid is pumped from the basement of the building (20) up to the rooftop of the building (20) and passed through the condenser coils, (27, 27A) where heat is transferred from the refrigerant fluid to the air drawn through the coils, (27, 27A) by the fans (29 and 31).

The illustrated air cooled condenser uses induced draught counter-flow to draw air through the tower (23). In this configuration, the fans ((29), 30) are located at the air outlet of the condensers (27, 27A). Air enters the tower (23) and is drawn vertically through the condenser (27) in a direction opposite to the flow of cooling fluid through the condensers (27, 27A).

Referring now to FIG. 2 there is shown a second form of closed circuit cooling system arrangement (32) which provides air conditioned air to a building (34). This cooling system arrangement (32) can include a roof top mounted heat exchanger (35) with a closed circuit cooling arrangement.

The illustrated cooling system arrangement (32) is similar to that described in relation to FIG. 1, in that it includes an enclosed circuit of refrigerant fluid (36) that is passed through a condenser (38) and an evaporator (40) by a compressor (42). The flow of fluid through the enclosed circuit (36) is controlled by an expansion valve (44). The evaporator (40) includes an enclosed water circuit (46) which has thermal energy removed therefrom in order for the enclosed water circuit (46) to be used to effect cooling of the air in the building (34) in a similar manner as described previously. The condenser (38) operates as a heat exchanger to extract thermal energy from the closed loop of refrigerant fluid (36).

The removal of thermal energy from the enclosed loop of refrigerant fluid (36) in the condenser (38) is effected by the use of cooling fluid which is drawn into the condenser (38) through tubing (50) and carried out of the condenser (38) through tubing (48). Cooling fluid is drawn into the condenser (38) and passed through it under the control of pump (51). Cooling fluid emitted from the condenser (38) is carried by tubing (48) to the rooftop of the building (34) where it enters a rooftop mounted closed circuit heat exchanger (52) of the closed circuit roof top mounted heat exchanger (35). The closed circuit roof top mounted heat exchanger (35) includes electrically driven fans (54 and 56) that operate to draw air therethrough.

The tubing (not illustrated in any detail in FIGS. 1 and 2) of the closed circuit heal exchanger (52) is generally thermally conductive and formed in a tortuous path disposed in a region that will be subject to air flow as air is drawn through the closed circuit heat exchanger (52). As can be appreciated, sections of the tubing can include thermally conductive extensions to improve the convective heat transfer efficiency as air passes over the tubing. Usually, thermally conductive extensions comprise heat fins that are usually formed from a suitably thermally conductive material. Having passed through the portion of tubing formed in a tortuous path the water is then carried out of the rooftop mounted closed circuit heat exchanger (52) through down pipe (50) and is pumped into the condenser (38) using the pump (51).

In addition to passing cooling fluid through a portion of tubing subject to forced airflow, the roof top mounted heat exchanger (35) also includes an air cooler (57). The air cooler (57) includes moistened water absorbent material located upstream of the air inlets of the closed circuit, heat exchanger (52). Operation of the fans (54, 56) draws air through the moistened water absorbent material of the air cooler (57) causing moisture in the water absorbent material to evaporate. The energy required to evaporate the moisture is extracted from the air, thus cooling the air prior to passing same through the closed circuit heat exchanger (52). The resulting cooler air allows for a greater temperature change when passing through the closed circuit heat exchangers (52) and therefore increases the effectiveness of roof top mounted heat exchanger (35) in removing thermal energy from the water flowing through the closed circuit heat exchanger (52).

FIGS. 3 to 6 show one exemplary form of a first closed circuit heat exchanger (60) of a heat exchange unit which can be used in closed circuit roof top mounted heat exchangers (23). As illustrated, the closed circuit heat exchanger (60), in this embodiment, is configured in a generally tubular shaped coil with a nominal longitudinal axis (62) X-X (best shown in FIGS. 4 and 5). The tubular coil (62) is configured with a generally square lateral cross-sectional area (i.e. perpendicular to the axis X-X) as best shown in FIG. 3. The square lateral cross-section has rounded corners. The tubular coil (62) does not extend completely around the longitudinal axis X-X, but rather has a longitudinal gap (64) at one corner thereof. At the longitudinal gap (64) there is positioned a longitudinally arranged header arrangement (66) (best seen in FIG. 6) which includes inlet (68) and outlet (70) ports to the heat exchange coil (60). The header arrangement (66) comprises two longitudinally orientated headers (72) and (73), the supply header (72) having an upper side mounted inlet tube (74) and the return header (73) having a lower side mounted outlet tube (75). Of course, in other embodiments, the inlet tube (74) and outlet tube (75) may be connected by a common header arrangement. The heat exchange coil (60) and header arrangement are mounted on a square base platform (78), which is typically constructed from galvanised steel, reinforced concrete or the like.

The gap (66) in the first heat exchanger (60) forms two longitudinal ends (76) and (77) of the heat exchange coil (60) between which a plurality of circumferentially arranged thermally conductive tubing (79) extend. The ends of each circumferential portion of tubing (79) is interconnected at various parts at each end using a U-bend junction (80) to form a tortuous path carrying water from the supply header (72) to the return header (73). The tubing (79) is mounted on a frame structure (82) mounted in the base platform 78 which provides a predetermined spacing between each circumferential length of tubing (79). This spacing is selected to allow air cooled by the air cooler to flow from the outside of the first closed circuit heat exchanger (60) through the sides of the closed circuit heat exchanger (60) and over the tubing (79).

In operation, a cooling fluid such as water, ammonia or Freon enters the closed circuit heat exchanger (60) through the supply header (72) via inlet tube 74 and flows through the tubing (79). Cooled air is forced over the tubing (79) through the action of fans (for example fans (29 and 31)) in the embodiment shown in FIG. 1 or fans (54 and 56) in the embodiment shown in FIG. 2 transferring heat from the water in the tubing (79) to the tubing (79) (generally conductive heat transfer) through to the air (generally convective heat transfer). The water in the tubing (79) is cooled and then is emitted from the first closed circuit heat exchanger (60) through the return header (73) via outlet tube (75).

FIGS. 7 and 8 show two preferred embodiments of a heat exchange unit (82) and (84) incorporating a closed circuit heat exchanger according to the present invention.

Referring first to the embodiment shown in FIG. 7, there is shown a front elevation view of a low noise heat exchange unit (82). The heat exchange unit (82) is a self contained unit which can be used individually or be coupled together with similar heat exchange units (82) to form a heart exchange system for use in a roof top mounted heat exchanger structure (23, 35) on a roof of a building (20, 34), such as is illustrated in FIGS. 1 and 2. The heat exchange unit (82) includes a first closed circuit heat exchanger (60) as previously described. The first closed circuit heat exchanger (60) is mounted on a base plate (85) constructed from sheets and sections of galvanised steel. Vertically above the first closed circuit heat exchanger (60) is positioned a centrally mounted electrically driven fan (86) arranged to draw cooled air through the sidewalls of the first closed circuit heat exchanger (60). The fan (86) is centrally mounted with its fan blade (87) rotatable about an axis which in turn is substantially aligned with the longitudinal axis X-X of the closed circuit heat exchanger (60). The fan (86) is orientated with the fan blades (87) directed downwardly away from the fan motor (87A) toward the interior of the closed circuit heat exchanger (60). In order to reduce vibration and noise caused by the operation of the fan (86), the fan (86) is mounted in a cylindrical attenuating drum (88) formed from a dampening material such as rubber or the like.

Arranged at two sides outward of the side walls of the closed circuit heat exchanger (60) are located two substantially planar air coolers (89 and 90). The air coolers (89, 90) are formed from moisture absorbent material which, which in one embodiment, retains water when moisture is drip fed onto the air coolers (89 and 90) using a distribution arrangement (not illustrated). The air coolers (89 and 90) are suspended over the side walls, which form the air inlets of the closed circuit heat exchanger (60) such that cooled air passing over the tubing (79) of the heat exchange coil (62) is required to pass first through the air coolers (89 and 90). As described previously, evaporation of the moisture extracts thermal energy from the air passing through the air coolers (89 and 90) and therefore cools this air. The extent to which air is cooled depends upon the ambient temperature and humidity of the external air.

In an embodiment, a water absorbent material pad comprising a plurality of fluted apertures of a size less than 7 mm in diameter is used for the air coolers (89 and 90).

It should be understood that the air coolers (89 and 90) are typically moistened by the application of water to the top of each of the air coolers (89 and 90) using a moisture distributor (not illustrated) such as for example a control valve or the like. The water applicator typically dispenses water over the top of air coolers (89 and 90). The water applied by the water applicator eventually trickles down through the air coolers (89 and 90) substantially wetting the entire material of the air coolers (89 and 90). In the event that the air coolers (89 and 90) do not fully absorb water applied to them, run-off from the bottom of each air cooler (89 and 90) may be collected in a tank (not illustrated) that may be returned to the water applicator via a pump (also not illustrated). In some exemplary embodiments, the run-off from the bottom of the air coolers is not recirculated to the top of the air cooler.

Referring now to the embodiment shown in FIG. 8, there is shown a front elevation view of a standard configuration heat exchange unit (84). Like the heat exchange unit shown in FIG. 7, this unit (84) is a self contained heat exchange unit which can be used individually or be fluidly connected together with similar heat exchange units (such as that shown in FIG. 7 or 8) to form a heat exchange system with a greater heat exchange capacity as compared with a single self-contained heart exchange unit. A structure such as that detailed in FIG. 7 or 8 may be constructed on a roof of a building, such as is illustrated in FIGS. 1 and 2. The structure of the heat exchange unit (84) is very similar to that described for the heat exchange unit (82) shown in FIG. 7 and includes a closed circuit heat exchanger (60) as previously described, a fan (92), air coolers (93 and 94) mounted on a base plate (85A). The difference between the two embodiments shown in FIGS. 7 and 8 relate to the orientation of the fan (92) and the configuration of the mounting section (91) in which the fan (92) is located. In this embodiment, the fan (92) is still centrally mounted with its fan blade (95) rotatable about an axis which is substantially aligned with the longitudinal axis X-X of the closed circuit heat exchanger (60). However, the fan (92) is not mounted in a cylindrical attenuating drum (88), but rather a cavity having a larger diameter D than the internal diameter E of the closed circuit heat exchanger (60). This allows the fan (92) to have a wider blade (95) and therefore draw a higher volumetric flow rate through the closed circuit heat exchanger (60) as compared to the smaller fan (86) of the heat exchange unit (82) shown in FIG. 7. In addition, the fan (92) is orientated with the fan blades (95) directed upwardly away from the fan motor (95A) and the interior of the closed circuit heat exchanger (60).

The heat exchange unit (82 and 84) shown in FIGS. 7 and 8 can be connected with other similar heat exchange units (82, 84) to form a modular heat exchange system. FIGS. 9 to 12 shows the plan views of various modular arrangements of the heat exchange units (82, 84), which will be referred to with reference to the reference numbers of heat exchange unit (82) for ease of description. It should be understood that these figures could equally be applicable to the heat exchange unit shown in FIG. 8.

FIG. 9 shows a plan of a single heat exchange unit (82), the heat exchange unit (82) includes a circular tubular closed circuit heat exchanger (60′). It should be understood that this tubular closed circuit heat exchanger (60′) has all the same elements as the closed circuit heat exchanger (60) illustrated in FIGS. 3 to 6 but has a generally circular lateral cross-section rather than a generally square lateral cross-section. FIGS. 10, 11 and 12 show the heat exchange unit (82) being interconnected into a series of two, three and four heat exchange units (82) respectively.

The heat exchange units (82, 84) can be connected in series or parallel, and in one embodiment, have an isolation circuit or fixtures between each heat exchange unit (82, 84) allowing each individual heat exchange unit to be isolated and taken off line for maintenance or replacement, while allowing the remaining heat exchange units to still function. Accordingly, during such maintenance periods the roof top mounted heat exchanger having these heat exchange units (82, 84) could still operate with a reduced capacity.

In a particular application, the number of heat exchange units (82, 84) would be selected to meet the maximum heat loading of a particular building or structure. In this respect, the individual thermal capacity of the heat exchange units (82, 84) would be known, and the maximum total thermal load from the air conditioning system of the building can be estimated. The maximum capacity would generally be estimated for the peak temperature loadings in summer. The number of heat exchange units (82, 84) used on the building would be selected to satisfy this maximum capacity.

In an exemplary embodiment, the size of the each heat exchange unit (82, 84) shown in FIGS. 7 to 12 is dimensioned to allow that heat exchange unit (82, 84) to fit into a standard goods lift. Typical dimensions would be for example 1420 mm wide, 1420 mm long and 2015 mm high. These dimensions would allow the heat exchange unit (82, 84) to be installed by loading the heat exchange unit (82, 84) in to a goods lift in a building to move the heat exchange unit (82, 84) from the ground floor to the roof of the building to where it is to be located. This can reduce installation costs as compared with existing heat exchange systems, which are generally large apparatus which need to be lifted onto the roof of, a building using specialised lifting equipment such as cranes. As can be appreciated, this can be an expensive exercise due to the hiring of the crane and permits and compliance formalities involved in positioning the crane at the base of a building, blocking roads and the like and lifting equipment therefrom.

As can be seen in FIGS. 7 to 12, each heat exchange unit (82, 84) has its own base structure (85, 85A) and accordingly in most applications it is not necessary to construct a new mounting structure on the roof the building, but rather the heat exchange unit can be bolted or otherwise fixed to the existing roof structure.

In some embodiments, the air coolers (89 and 90) of each heat exchange unit (82, 84) are only operable when the ambient air temperature surrounding the heat exchange unit is above a predetermined temperature. In these embodiments, the heat exchange units (82 and 84) can include a controller that activates the use of the air coolers (89 and 90). For example, the control methodology could wet the air coolers (89 and 90) for a short period of time on a regular or periodic basis when the temperature of the cooling fluid emitted from the closed circuit heat exchanger rises above a first pre-determined limit. For example, the first predetermined limit could be 24° C. The air coolers (89 and 90) would be wetted when cooling fluid temperature is above the first limit until such time that the temperature of the cooling fluid emitted from the closed circuit heat exchanger drops below a second predetermined limit. The second predetermined limit is preferably at least 2° C. below the first predetermined limit temperature to avoid the dispensers being constantly activated and deactivated in response to small fluctuations in the temperature of the cooling fluid around the predetermined limits.

Alternative control methodologies could be employed with the objective being to operate the air coolers (89 and 90) for the least required time to accommodate the requirement for an increased cooling capacity for the period of time that the increased cooling capacity is required.

In other embodiments, variable pitch fans are used to draw air through the first closed circuit heat exchanger and the air coolers.

A range of cooling fluids other than water could be used in the closed circuit of a heat exchanger. In one alternative embodiment, the cooling fluid comprises highly concentrated ammonia with a first closed circuit heat exchanger comprising stainless steel or aluminium tubing effecting passage of the ammonia through the closed circuit heat exchanger. Further, a range of materials could be used to form the passages for the cooling fluid such as mild steel. As is understood in the art, the improved cooling effect of a heat exchanger according to the present invention enables the construction of a heat exchanger, comprising an ammonia cooling fluid, of a reduced physical size with a similar cooling capacity as that for larger sized conventional heat exchangers. As a result, closed circuit heat exchangers using ammonia as the cooling fluid become a more economically feasible option for relatively small installations.

FIG. 13 shows an embodiment of the heat exchange unit (102) with the closed circuit heat exchanger having four heat exchanger bodies (104) which comprises first, second, third and fourth heat exchangers. The closed circuit heat exchangers are in fluid communication through connecting channels (106). In this embodiment each of the heat exchanger bodies (104) has next to it an air cooler (112) located upstream of the closed circuit heat exchanger (104). Also shown is a fan arrangement (110) which causes air to pass through the closed circuit heat exchangers and the air coolers. In this embodiment, the fan arrangement has one fan (108) which is a six bladed fan.

FIG. 14 shows a detail of the heat exchange unit of FIG. 13 where an supply header (114) is shown above one of the closed circuit heat exchangers for the inflow of cooling fluid to the closed circuit heat exchanger (104).

FIG. 15 is a side view of one embodiment of a heat exchange unit (102). In this embodiment the closed circuit heat exchanger (104) is a duplex closed circuit heat exchanger which has a first heat exchanger body (116) and a second heat exchanger body (118) which are substantially parallel to each other so that air which is caused to pass through the closed circuit heat exchanger passes over both the heat exchanger bodies. Cooling fluid flows in at a first supply header (120) which then flows up the first heat exchanger body (116) until it reaches a first outlet header (122). This first outlet header (122) is in cooling fluid communication with a second supply header (124) for the second heat exchanger body (118). The second supply header (124) allows cooling fluid to flow down through the second heat exchanger panel until it reaches a return header (126). The cooling fluid may then flow to another closed circuit heat exchanger in the heat exchanger unit (102), alternatively it may flow to another closed circuit heat exchanger in another heat exchanger unit (not shown), further alternatively it may flow out to another part of the cooling system arrangement shown in FIG. 1.

FIG. 16 shows a different orientation of the heat exchanger unit shown in FIG. 13.

FIG. 17 shows a different orientation of the detail of the heat exchange unit as shown in FIG. 14.

The different orientations of the heat exchange units may be used to enhance exposure of the heat exchangers and/or the air coolers to ambient air. This may enhance the inflow and cooling characteristics of the heat exchange unit, especially when used as a module in a modular heat exchange system of heat exchange units.

FIG. 18 is a side cross sectional view of a heat exchange unit (102) showing a fan arrangement (110) at the top of the heat exchange unit and two closed circuit heat exchangers (104) and two air coolers (112) at sides of the heat exchange unit.

FIG. 19 shows an embodiment of a closed circuit heat exchanger showing a planar side (130) of the heat exchanger body (131).

FIG. 20 is a side view of the heat exchanger body (131) as shown in FIG. 19 with planar sides facing both left (132) and right (130) relative to the page.

FIG. 21 shows a plan view of a modular heat exchange system (160)) with eight heat exchange units (102). Cooling fluid is supplied to the modular heat exchange system via a heat exchange system supply pipe (140). Each heat exchange unit (102) has an inflow of cooling fluid from the heat exchange system supply pipe (140) via a heat exchange unit supply pipe (142). The cooled cooling fluid flows out from each of the heat exchange units (102) via a heat exchange unit return pipe (152). Each of the heat exchange unit return pipes (152) allows the cooled cooling fluid to flow into the heat exchange system return pipe (150). In the figure the direction of flow of the cooling fluid has been marked on the pipes with arrows.

With reference to FIG. 22, a diagrammatic representation of a modular heat exchange system arrangement is provided wherein cooling fluid is passed through closed circuit heat exchangers (225, 230) through an supply pipe (215) and subsequent to passing through the closed circuit heat exchangers (225, 230) is emitted through an return pipe (220). The cooling fluid may be water or a refrigerant fluid that is used to transfer thermal energy such as Freon. Further, where the cooling fluid is water, additives such as Glycol may be added to attempt to prevent freezing of the cooling fluid. The cooling fluid is supplied to the closed circuit heat exchangers (225, 230) through the supply pipe (215) for the purpose of cooling the cooling fluid and during the passage through the closed circuit heat exchangers (225, 230) thermal energy is extracted from the cooling fluid such that the fluid emitted through the return pipe (220) has a substantially lower temperature and hence may be returned to a part of the cooling system that uses the fluid for the purpose of absorbing and transferring thermal energy.

During periods where the ambient air temperature is sufficiently low, air is drawn through the closed circuit heat exchangers (225, 230) without the operation of the air cooler. In this instance, the modular heat exchange system (210) is described as running in the “dry” mode and thermal energy is extracted from the cooling fluid solely by the action of passing air through the closed circuit heat exchangers (225, 230) as the cooling fluid (water/refrigerant) passes through the closed circuit, heat exchangers (225, 230).

However, during periods where the ambient air temperature is not sufficiently low, or an increased heat exchange capacity is required that may not be effected by operating a closed circuit heat exchanger in the “dry” mode; moisture absorbent material in the form of air coolers (35, 40) are moistened by a moisture (preferably with water) in order to effect evaporative cooling of the air prior to the passage of same through the closed circuit heat exchangers (25, 30).

In the event that the air cooler is completely dry and has no water in the troughs (255, 260) then the water make-up solenoid valve (270) is opened in order to introduce external make-up water into the troughs (255, 260) through conduits (267, 265). The external make-up water is provided to the water make-up solenoid valve (270) through an inlet conduit (272). A back pressure flow prevention device (273) may be included depending upon local installation regulations.

The troughs (255, 260) include a water level monitoring device generally in the form of a flotation device that monitors the water level in the troughs (255, 260). Once there is a sufficient water level in the troughs to maintain a positive head of pressure to the inlet of the pump (245) then the pump may be operated to pump water through a conduit (246) and provide same to water distribution arrangements (247, 250) for distribution of the water to the upper portions of the air coolers (235, 240).

Of course, as water trickles down through the air coolers (235, 240) under the action of gravity the moisture absorbent material in the air cooler absorbs the water and once saturated any additional water provided to the air coolers (235, 240) will run-off the moisture absorbent material. Ultimately, any run-off water will be collected in the troughs (255, 260). The troughs (255, 260) have an overflow mechanism (280, 285) in the event that there is a continuing supply of run-off water entering the troughs (255, 260) despite the float monitoring device detecting a sufficient water level in the trough and deactivating the water make-up solenoid valve (270). Over time, as the evaporative cooling system operates, water is evaporated as it cools the ambient air passing through the air coolers (235, 240) and any water lost through vaporization is replaced by operation of the water make-up solenoid valve (270) in conjunction with the float monitoring device in the troughs (255, 260). The moisture recirculation system continues to operate as long as the modular heat exchange system (210) is required to operate in “wet” mode.

A water dump valve (275) is also connected to the troughs (255, 260) by a conduit (265). The water dump valve is operated on a regular basis for the purpose of dumping the contents of the troughs (255, 260) to reduce the potential for the generation and growth of bacteria that may result from an increase in concentration of sediment and/or impurities in the troughs (255, 260). This is particularly the situation when water is used as the moisture.

The particular arrangement of a recirculation system detailed in FIG. 22 is very common and has been used successfully for many decades. However, this standard arrangement of a moisture recirculation system has disadvantages including a relatively large trough capacity. In this respect, FIG. 22 is an end perspective and the troughs (255, 260) extend the entire length of the air coolers (235, 240). In, the event that the closed circuit heat exchanger is relatively long, the sump capacity is commensurably large and in order to maintain a positive head of water pressure at the inlet side of the pump (245) it is necessary to maintain a minimum depth of water in the troughs (255, 260). For a relatively long trough, maintaining the minimum depth may represent a substantial amount of water. Further, a separate disadvantage of existing arrangements is the relatively long period of time that is required to transition the modular heat exchange system (210) from “dry” to “wet” mode as a result of the supply of external make-up water to the troughs (255, 260).

An embodiment of the present invention with a moisture recirculation system for wetting the air coolers is detailed in FIG. 23 which provides a diagrammatic representation from a similar end perspective as that of FIG. 22.

With reference to FIG. 23, a cooling fluid that requires cooling is provided to closed circuit heat exchangers (325, 330) through a supply pipe (315). As the fluid passes through the closed circuit heat exchangers (325, 330) thermal energy is extracted therefrom and cooled cooling fluid is emitted from the bottom of the closed circuit heat exchangers (325, 330). Cooled cooling fluid is returned through a return pipe (320). Just as for the arrangement detailed in FIG. 22, the modular heat exchange system (300) extracts thermal energy from the cooling fluid by passing same through the closed circuit heat exchangers (325, 330) whilst passing ambient air through the closed circuit heat exchangers. In the event that the ambient air temperature is not sufficiently low, or an increased heat exchange capacity is required, the device detailed in FIG. 23 is transitioned from “dry” mode to “wet” mode by the application of moisture (preferably water) to the air coolers (335, 340) such that the air coolers evaporatively cool the ambient air. The cooled air then passes through the closed circuit heat exchangers (325, 330).

In the arrangement detailed in FIG. 23, when seeking to transition the arrangement to “wet” mode, the water make-up solenoid valve (370) is activated to allow external water that is supplied through conduit (372) to pass through conduits (346 and 349) until the external make-up water reaches and passes through the water distribution arrangements (348, 350). The external make-up water then trickles down through the moisture absorbent material of the air coolers (335, 340) and is absorbed by same. As ambient air passes through the air coolers (335, 340) the air is cooled by the action of evaporation as the water that was initially absorbed by the moisture absorbent material is then vapourised and converted from liquid to gaseous form.

In order to ensure that the air coolers (335, 340) are completely saturated, a sufficient amount of water is provided to the water distribution arrangements (348, 350) such that water trickles down through the evaporative air coolers (335, 340) and runs-off the air coolers into the respective collecting troughs (355, 360). The collecting troughs (355, 360) act as a temporary and intermediate collection of run-off water which is then provided, through conduits to the sump (365). The sump does not need to extend the full length of the air coolers (335, 340) and may be dimensioned to have a capacity that is substantially smaller as compared with the standard trough capacity (as detailed in FIG. 22). The sump (365) collects the run-off water from the collecting troughs (355, 360) and upon collecting enough run-off water to provide a sufficient head of pressure to the intake of the pump (345) then the pump may be activated to pump run-off water up through conduits (346, 349) and re-distribute the water collected in the sump (365) to the water distribution arrangements disposed above the air coolers (348, 350). A back pressure flow prevention device (347) may be included.

The water make-up solenoid valve (370) may be activated as a result of a water level monitoring device in the form of a flotation device in the sump (365). A back pressure flow prevention device (371) may be included. In any event, as water is depleted from the evaporative air cooling system, the water level in the sump (365) decreases and when sufficiently low (such that a positive head of pressure will not be maintained at the pump intake) the make-up solenoid valve (370) is activated to introduce replacement make-up water into the system. In the embodiment of FIG. 23, the make-up water is deposited directly onto the top of the air coolers where it is most directly needed. As run-off is collected in the collecting troughs (355, 360) and passed to the sump (365), the water level in the sump increases.

Again, as for the apparatus detailed in FIG. 22, upon expiry of a period of time the water dump valve (375) is activated to release the entire contents of the sump (365) to reduce the likelihood of the generation and growth of bacteria and slime in the sump (365). However, as the sump (365) is dimensioned to have a substantially lower capacity as compared with the sump of a standard arrangement, the amount of water that is discharged as a result of a dumping operation is commensurately substantially less.

In embodiments where the make-up water is provided directly to the water distribution arrangements (348, 350) thus effectively, by-passing the sump (365), the arrangement provides even less delay in achieving fully saturated air coolers (335, 340) as compared with the existing arrangements.

With reference to FIG. 24, a perspective view of the cooling system of FIG. 23 is provided. The same parts in FIGS. 23 and 24 are identified by use of the same identification number.

FIG. 24 details various parts of the cooling system in perspective and of particular importance is the extension of the collecting troughs (355, 360) extending the entire length of the air coolers (335, 344). Further, the water collected by the collecting troughs (355, 360) is subsequently passed to the sump (365) for collection and storage. As will be noted in FIG. 24, the dimensions of the sump (365) are substantially smaller as compared with the dimensions of the collecting troughs (355, 360) and therefore, the sump (365) has a significantly reduced volumetric capacity as compared with the collecting troughs (355, 360). Accordingly, if the troughs (355, 360) were used to collect and store run-off, it would require substantially more water (as compared with the sump (365)) to maintain a minimum head of pressure at the intake of a pump.

In industrial and commercial applications, the air coolers (335, 340) can be relatively large. In these applications, it is not unusual for the air coolers (335, 340) to comprise a number of smaller cooling pads that are placed abutment with one another thus forming a wall that extends for a sufficient length and height to substantially conform with the dimensions of the closed circuit heat exchangers (325, 330). Accordingly, the collecting troughs (355, 360) must extend along the full length of the air coolers (335, 340) in order to collect any water run-off from the air coolers (335, 340).

However, in the embodiment of FIGS. 23 and 24, the collecting troughs (355, 360) may act as a temporary collection and storage means for water run-off and may pass run-off water to the sump (365) for collection and storage. As a result, the volumetric water holding capacity of the collecting troughs (355, 360) can be substantially reduced as compared with existing collection and storage troughs that must both collect and store run-off water and maintain a sufficient head of pressure at a pump intake:

Having passed run-off water to the sump (365) the water is pumped (345) up through backflow pressure prevention device (347) and through the conduits to the water distribution arrangements (348, 350) whereby water is distributed to the upper portion of the air coolers (335, 340).

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form or suggestion that the prior art forms part of the common general knowledge of persons skilled in the relevant field of technology at the priority date of the claims herein. 

1-38. (canceled)
 39. A heat exchange unit for use in a modular heat exchange system including: at least one first heat exchanger having a closed circuit for cooling fluid; at least one air cooler located upstream of the first heat exchanger; at least one first fan arrangement operable to cause air to pass through the at least one air cooler and the at least one first heat exchanger; and at least one channel providing cooling fluid interconnection between the first heat exchanger and, when in use in the modular heat exchange system, a heat exchanger in at least one other heat exchange unit wherein the heat exchanger in each heat exchanger unit is a microchannel heat exchanger.
 40. A heat exchange unit according to claim 39, wherein the at least one first heat exchanger includes at least one fluid carrying passage, and wherein the fluid carrying passage type is any one of plate, plate-fin, spiral, tube, double-pipe or coil arrangement.
 41. A heat exchange unit according to claim 39, wherein the at least one first heat exchanger includes at least one first and at least one second microchannel heat exchanger modules.
 42. A heat exchange unit according to claim 41, wherein the at least one first and second heat exchanger modules are arranged such that surfaces of the first module are substantially parallel to surfaces of the second module, and the first module and the second module are aligned such that flow of the air passes through the first module and subsequently through the second module, and wherein the cooling fluid is arranged to flow through the first module and subsequently through the second module.
 43. A heat exchange unit according to claim 39, wherein the at least one first heat exchanger includes fluid carrying passages extending between vertical sides of the at least one first heat exchanger.
 44. A heat exchange unit according to claim 39, wherein the cooling fluid is any one or more of water, oil, ammonia, Freon and carbon dioxide.
 45. A heat exchange unit according to claim 39, wherein the at least one first heat exchanger is configured such that it forms a substantially cross-sectional tubular arrangement with an internal space through which the air can pass.
 46. A heat exchange unit according to claim 45, wherein the tubular arrangement has a substantially cross-sectional shape including any one of: generally square, generally hexagonal, generally octagonal, generally star-shaped, generally triangular, generally circular, generally rectangular and generally oval.
 47. A heat exchange unit according to claim 45, wherein the tubular arrangement has a structure which extends circumferentially wholly around the longitudinal axis of the tubular arrangement.
 48. A heat exchange unit according to claim 45, wherein the tubular arrangement has a structure which extends circumferentially partially around the longitudinal axis of the tubular arrangement.
 49. A heat exchange unit according to claim 45, wherein the tubular arrangement forms a continuous body around the longitudinal axis.
 50. A heat exchange unit according to claim 45, wherein the at least one first heat exchanger includes a heat exchange body, and wherein the heat exchange body extends partially around the longitudinal axis of the tubular arrangement.
 51. A heat exchange unit according to claim 50, wherein the closed circuit is formed by a plurality of circumferentially arranged passages that are generally laterally arranged in the heat exchange body relative to the longitudinal axis.
 52. A heat exchange unit according to claim 45, wherein the at least one first fan arrangement is operable to cause air to pass longitudinally through the internal space of the tubular arrangement.
 53. A heat exchange unit according to claim 45, wherein the at least one first fan arrangement is positioned at one end of the tubular arrangement.
 54. A heat exchange unit according to claim 45, wherein the at least one first fan arrangement causes the air to pass through walls of the tubular arrangement.
 55. A heat exchange unit according to claim 39, further including a header arrangement for allowing the cooling fluid to enter and to exit the closed circuit.
 56. A heat exchange unit according to claim 39, further including a header arrangement for allowing the cooling fluid to enter and to exit the closed circuit, wherein the at least one first heat exchanger is configured such that it forms a generally square, generally hexagonal, generally octagonal, generally star-shaped, generally triangular, generally circular, generally rectangular and generally oval cross-sectional tubular arrangement with an internal space through which the air can pass, and the header arrangement includes a header provided at or near one longitudinal end of, and generally parallel to the longitudinal axis of the tubular arrangement.
 57. A heat exchange unit according to claim 39, further including a header arrangement for allowing the cooling fluid to enter and to exit the closed circuit, wherein the at least one first heat exchanger is configured such that it forms a generally square, generally hexagonal, generally octagonal, generally star-shaped, generally triangular, generally circular, generally rectangular and generally oval cross-sectional tubular arrangement with an internal space through which the air can pass, and the header arrangement includes a header provided at both of two spaced apart longitudinal ends of the tubular arrangement, and wherein each of the headers extend generally parallel to the longitudinal axis of the tubular arrangement.
 58. A heat exchange unit according to claim 55, wherein the cooling fluid flows through the at least one first heat exchanger by entering the header arrangement at the top end of the at least one first heat exchanger and exiting the header arrangement at the base end of the at least one first heat exchanger.
 59. A heat exchange unit according to claim 55, wherein the header arrangement includes a substantially horizontal supply header provided at or near the top of the at least one first heat exchanger and a substantially horizontal return header provided at or near the bottom of the at least one first heat exchanger; and, wherein the cooling fluid is supplied through the supply header and passed through the at least one first heat exchanger to the return header.
 60. A heat exchange unit according to claim 39, wherein the air cooler includes a moisture absorbent material in the form of moisture absorbent pads, and wherein the air cooler, when in use, is maintained moist with moisture such that the air passing through the air cooler is cooled by the action of evaporation prior to passing over a portion of the at least one first heat exchanger.
 61. A heat exchange unit according to claim 60, wherein the moisture absorbent material includes a plurality of fluted apertures.
 62. A heat exchange unit according claim 60, wherein the moisture absorbent material supports an adiabatic process.
 63. A heat exchange unit according to claim 60, wherein the moisture is water.
 64. A heat exchange unit according to claim 63, wherein the water includes anti-microbial additives.
 65. A heat exchange unit according to claim 60, further including a moisture recirculation system including: a moisture distribution arrangement, when in use, for distributing the moisture to an upper portion of the moisture absorbent material; a trough disposed below the lower most portion of the moisture absorbent material for initially collecting moisture run-off; a sump in fluid communication with the trough for collecting and storing the run-off; and, a pump in fluid communication with the sump which, when in use, transfers the moisture from the sump to the moisture absorbent material.
 66. A heat exchange unit according to claim 65, further including an external source of make-up moisture in fluid communication with the moisture recirculation system where any supply of make-up moisture is supplied directly to the moisture absorbent material.
 67. A heat exchange unit according to claim 65, wherein the moisture transferred from the sump to the moisture absorbent material is effected by transferring moisture to the moisture distribution arrangement.
 68. A heat exchange unit according to claim 66, wherein the make-up moisture is supplied to the moisture distribution arrangement.
 69. A heat exchange unit according to claim 39, further including at least one second heat exchanger having a dosed circuit for cooling fluid.
 70. A heat exchange unit according to claim 69, wherein the at least one first heat exchanger is configured such that it forms a generally square, generally hexagonal, generally octagonal, generally star-shaped, generally triangular, generally circular, generally rectangular and generally oval cross-sectional tubular arrangement with an internal space through which the air can pass, and the at least one first heat exchanger and the at least one second heat exchanger are configured such that they form the tubular arrangement.
 71. A heat exchange unit according to claim 69, wherein the at least one first and the at least one second heat exchangers are aligned substantially in series from an air flow perspective, thereby forming a heat exchanger stack.
 72. A heat exchange unit according to claim 69, wherein the at least one first and the at least one second heat exchangers are arranged in parallel.
 73. A modular heat exchange system including: at least two heat exchange units each having a first heat exchanger having a closed circuit for cooling fluid; at least one air cooler forming a second heat exchanger located upstream of the first heat exchanger, and at least one first fan arrangement operable to cause air to pass through the at least one air cooler and the first heat exchanger, wherein the first heat exchangers of each of the at least two heat exchanger units are micro-channel heat exchangers and in fluid communication allowing flow of cooling fluid therebetween.
 74. A modular heat exchange system including: at least two heat exchange units, each heat exchange unit being in accordance with claim 39, wherein the at least one first heat exchangers of each of the at least two heat exchange units are in fluid communication allowing flow of cooling fluid therebetween.
 75. A method of circulating moisture for evaporatively cooling air in a moisture recirculation system according to claim 66, the method including the steps of: applying the moisture to the upper portion of the moisture absorbent material; initially collecting the moisture run-off in the trough disposed below the moisture absorbent material; transferring the run-off moisture from the trough to the sump for storage; transferring the moisture from the sump to the moisture absorbent material; and monitoring the moisture level in the sump and in the event that the moisture level in the sump falls below a predetermined threshold, activating supply from an external source of make-up moisture and supplying said make-up moisture directly to the moisture absorbent material.
 76. A method of installation of a modular heat exchange system including: transporting one or more heat exchange units, according to claim 39, to an installation location; connecting the one or more heat exchange units to a cooling fluid supply; connecting the one or more heat exchange units to a power supply; and activating the modular heat exchange system. 